Women's 800m

South Africa's Caster Semenya, right and U.S. runner Alysia Johnson Montano, center, take off at the start of one of the Women's 800m heats at the London 2012 Olympic Games.

South Africa's Caster Semenya, right and U.S. runner Alysia Johnson Montano, center, take off at the start of one of the Women's 800m heats at the London 2012 Olympic Games. (Olivier Morin, AFP/Getty Images)

South Africa's Caster Semenya, right and U.S. runner Alysia Johnson Montano, center, take off at the start of one of the Women's 800m heats at the London 2012 Olympic Games.